The present invention relates to an improved hydrostatically compressed elastomeric shock absorber spring and method for its manufacture.
The production of hydrostatic compression springs, whose casing in the form of a bent flattened tube contains an elastomer under hydrostatic compression, is known.
However, one of the drawbacks of these springs of a bent tube shape (C-shaped or S-shaped) resides in their high flexibility, that is to say their tendency to be squashed particularly under the effect of a given static load. It follows that if the load varies, the squashing varies, which may be unsuitable for certain uses of the spring. This is particularly the case when these springs are employed to suspend an automobile vehicle body with respect to a chassis bearing the wheels.
It is known in addition that, by heating the mass of an elastomer enclosed in a deformable casing, this elastomer is expanded in this casing, which permits the elastic reaction of the so-constituted hydrostatically compressed elastomer spring to be regulated. It is thus possible to adjust the length of the spring and to render it constant whatever the variation in the load that it supports or the temperature variation that it undergoes.
Now, taking into account the shape itself of these springs, i.e., a S-shaped or C-shaped springs having very long lengths in relationship to their cross-sections, a heating of the elastomer must lead rapidly to thermal equilibrium and heating of the casing, which, after experimental observation, gives mediocre results as to the desired effect.
It has been realised, however, that if a metal core buried in the elastomer is used as an electrically resistant element, it was possible to transmit rapidly a flow of heat to the elastomer and to create transversely to the tube, a temperature gradient which, due to considerable thermal inertia and insulating power of the elastomer, remains constant. The desired object is then achieved under much better conditions.